Teachers have a lesbian threesome with students

The headmistress of the school asks the teacher and her two students to stay with her after school. It turns out that she found out that the girls are half-sisters and the teacher is their stepmother. In addition, she clearly preferred them in cute amusements. At the same time, the headmistress insists that the girls be punished in front of her eyes, and after that she herself takes part in group fun with this very unscrupulous family!